Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor light-emitting device and a method for producing a Group III nitride semiconductor, more specifically a method for forming a Group III nitride semiconductor containing In.
Background Art
A MQW structure in which an InGaN well layer and an AlGaN barrier layer are sequentially and repeatedly deposited, is widely used as a light-emitting layer of Group III nitride semiconductor light-emitting device. Since the barrier layer is formed of AlGaN, the growth temperature thereof must be higher than that of the well layer so as to obtain good crystallinity. Therefore, it is necessary to increase the temperature after the formation of the well layer, and then to grow the barrier layer. However, In is evaporated from the well layer due to heating, thereby resulting in reduction of emission efficiency or variation of emission wavelength. Therefore, a protective layer being grown at the same temperature as the growth temperature of the well layer is provided between the well layer and the barrier layer to prevent In evaporation.
Japanese Patent Application Laid-Open (kokai) No. 2010-80619 describes that a protective layer has a single layer structure of AlGaN or a layered structure of GaN and AlGaN. Moreover, Japanese Patent Application Laid-Open (kokai) No. 2012-216751 describes that a protective layer is formed of GaN having a thickness of 6 Å (0.6 nm). Further, Japanese Patent Application Laid-Open (kokai) No. 2001-332763 describes that a protective layer is formed of InGaN having an In composition ratio of 7 at % to 60 at %.
Since the protective layer is grown at the same temperature as employed for the well layer, the crystallinity thereof is low, resulting in reduction of emission efficiency. Therefore, the present inventors have studied to improve the crystal quality by incorporating a small amount of In as a surfactant (impurity to flatten the surface) in the protective layer. The amount of In is small because the incorporation of an excessive amount of In has the opposite effect, resulting in deterioration of crystal quality.
However, the protective layer is grown at a low temperature because it is grown at the same temperature as employed for the well layer. In is easily incorporated in the crystal at a low temperature, and a certain amount of In is included in the crystal even if the minimum amount of raw material gas as In source is supplied. Thus, a protective layer could not be formed of Group III nitride semiconductor having a low In composition ratio.